The present invention relates to implantable catheter electrodes and particularly to catheter electrodes that provide high effective length electrode structures utilizing electrode extension members which exhibit low electrical impedance.
The implantable cardioverter defibrillator (ICD) is a recognized and important therapy for patients with a propensity for ventricular fibrillation and hemodynamically-compromising tachycardias. Initially, ICD's required open-chest surgery to attach large electrodes, such as epicardial patch electrodes, to the epicardial surfaces of the heart. These procedures increased the mortality and expense associated with ICD implantation.
The present trend is towards the use of defibrillation catheters which, at a minimum, rest in the right ventricle of the heart. Unfortunately these catheter electrodes have higher electrical impedances than do the epicardial patches. This in turn demands a significantly increased voltage in order to provide a sufficient current for defibrillation. This current requirement results, therefore, in a significantly higher energy requirement for defibrillation.
The prior art defibrillation catheter electrodes have the maximum surface areas allowed by the anatomical constraints of the human heart. Nevertheless, their impedances are excessively high. There is, therefore, a need for a low impedance endocardial catheter electrode that will fit through the human veins and be able to reside in the right ventricle of the heart.
Mathematical analysis and laboratory testing has demonstrated that the surface area of a catheter electrode is not as important as is the electrode length for establishing a low impedance electrode. Thus, the object of the present invention is to provide a small diameter catheter electrode that has a large effective length.